Effects of Substance-P and Neuropeptide-Y onin VitroSteroid Release by Porcine Granulosa and Luteal Cells*

Abstract

The presence of substance-P (SP)- and neuropeptide-Y (NPY)-like immunoreactivity was recently shown in nerves that innervate the ovary. In the present in vitro study we demonstrate that both peptides have direct effects on ovarian steroidogenesis. In cultured porcine granulosa (G-) cells, neither peptide affected progesterone (P) production under basal conditions, but they both inhibited gonadotropin-stimulated P secretion. In luteal (L-) cell cultures, basal as well as hCG-stimulated P release were dose-dependently inhibited by NPY (ED50, 4 x 10(-9) M; identical for both, basal and stimulated release), while SP had only a moderate inhibitory effect (ED50, 6 x 10(-8) M). In the presence of AP13, a specific SP antagonist, the inhibitory effect of SP on P release was abolished, which suggests a receptor-mediated effect. In addition, we determined androstenedione (A) and estradiol (E2) release into G- and L-cell culture media. While E2 production in G-cell cultures was not influenced by SP and NPY, both peptides had a dose-dependent stimulatory effect on E2 secretion by L-cells. In contrast to E2 release, A secretion by G- as well as L-cell cultures was increased by gonadotropins. Both SP and NPY decreased gonadotropin-stimulated A secretion by G- and L-cells under basal as well as hCG-stimulated conditions. Furthermore, we demonstrate SP immunoreactivity in media of G- and L-cell cultures with a HPLC retention time identical to that of synthetic SP. This may suggest ovarian synthesis, in which case the peptide exerts auto- and/or paracrine effects on ovarian steroidogenesis. From these in vitro results we suggest that SP and NPY have a modulatory effect on ovarian function in pigs not only by their well known regulatory effects of blood supply, but also by a direct effect on ovarian steroidogenesis.